Autism spectrum disorder (ASD) is a lifelong neurodevelopmental disorder characterized by social deficits, impaired verbal and nonverbal communication and repetitive movements or circumscribed interests (see, for example, American Psychiatric Association (2013) Desk Reference to the Diagnostic Criteria from DSM-5, 5th ed. Washington, D.C.; American Psychiatric Association). About 1 in 68 children are identified with autism spectrum disorder according to estimates from CDC's Autism and Developmental Disabilities Monitoring (ADDM) Network (Centers for Disease Control and Prevention, 2014, MMWR Surveill Summn; 63:1-21). The current process for a clinical diagnosis includes establishing a developmental history and assessments of behavioral characteristics such as speech, language, intellectual abilities, and educational or vocational attainment. Patients can be reliably diagnosed through behavioral testing at age 2 years. However, for a variety of reasons, the average age of diagnosis is 4.5 years. It is increasingly recognized that detection of ASD at the earliest age possible age is important for initiating optimally effective intervention and results in better patient and family outcomes (Payakachat et al., 2012, Expert Rev Pharnmacoecon Outcomes Res; 12:485-503; and Thompson, 2013, J Appl Res Intellect Disabil; 26:81-107). Establishing personalized therapy for children with ASD at the earliest age possible improves outcomes including a higher level of cognitive and social function and improved communication as well as decreased financial and emotional burden on families (Dawson et al., 2010, Pediatrics; 125:e17-23; and Ganz, 2007, Arch Pediatr Adolesc Med; 161:343-349). Thus, the development of a biologically-based blood test to aid in the assessment of risk for a diagnosis of ASD at an early age would facilitate implementing intensive behavioral therapy at the earliest age possible and would be beneficial to patients, families and medical providers.